Skin aging may be largely classified into two types: the first type is chronologic aging of the skin which is unavoidable with the lapse of time; and the second type is photoaging of the skin. The photoaging is observed when the skin on the face, the back of the hand, and the posterior neck are exposed to the solar rays for a long time. The photoaging is caused by the chronologic aging and ultraviolet rays.
The photoaging relates with rough wrinkles, irregular pigmentary deposits, loss of skin elasticity, disturbance of skin barrier function, and cancer of the skin. The photoagaing can be prevented by avoiding the exposure to the ultraviolet rays. Recently, it is disclosed that the infrared rays which occupy 54% of solar energy are among the environmental factors for accelerating the skin aging by a thermal effect.
As the environmental contamination results in the depletion of ozone layer, the skin may be easily aging and damaged due to the increased exposure to the ultraviolet rays. In order to prevent the skin from being damaged by the ultraviolet rays, cosmetics with sunscreen added therein have been developed.
The sunscreen may be largely classified into organic-based sunscreen and inorganic-based sunscreen.
The organic-based sunscreen comprises ingredients with conjugated bond capable of absorbing the ultraviolet rays in a molecular structure. This organic-based sunscreen might cause problems of skin toxicity, allergy to the skin, and discoloration.
The inorganic-based sunscreen comprises powder for scattering the ultraviolet rays, for example, metal oxide with a high refractive index. In case of the inorganic-based sunscreen, the above problems caused by the organic-based sunscreen would not occur. Recently, the inorganic-based sunscreen is widely used in view of safety. However, the powder such as the metal oxide constituting the inorganic-based sunscreen has strong aggregation so that a lump of powder is increased in size due to the powder aggregation. In this case, the lump of powder with the increased size may deteriorate the feeling to the skin and the adhesion to the skin, and may lower the efficiency of sunscreen.
Accordingly, if using the inorganic-based sunscreen, it is necessary to overcome the above problems caused by the powder aggregation. However, a method for preventing the above problem of the powder aggregation has not been proposed yet.
There are many reports informing that the ultraviolet rays of the solar rays especially have adverse effects on the human body. Thus, blocking the ultraviolet rays was a matter of primary concern in the cosmetics. However, the newest reports disclose that the infrared rays also have adverse effects on the human skin. Thus, it needs to provide a method for preventing the skin from being damaged by the infrared rays, but there is no proposed method.